It is oftentimes essential in a variety of areas, for example the aerospace field, to have articles of manufacture and articles having a coating thereon which have low temperature expansion coefficients (TEC). Such articles have critical dimensions and for the satisfactory function of such articles it is necessary that such critical dimensions do not change during environmental changes such as temperature. Such articles include optical reflectors, microwave filters, feedhorns, wave guides and the like.
One known method of fabricating such articles involves machining them from low thermal expansion coefficient nickel-iron alloys such as INVAR (an alloy or iron and nickel containing about 36%, by weight of nickel and 64%, by weight, of iron). While this machining technique is time-consuming, costly, and ill-suited to mass production, it has been, and still is being, utilized rather than the more efficient and cost-effective technique of electroforming owing to the lack of a workable and practical method of electrodepositing INVAR and other low temperature coefficient alloys to any substantial thickness. In this regard, it should be noted that alloys of nickel and iron have been successfully electrodeposited, but only in the form of thin nickel and iron films for magnetic memory applications. Attempts to electrodeposit such alloys to thicknesses required for electroforming have been unsuccessful owing to the inability to control the proportions of the alloy constituents in the thicker electrodepositions or electroformed articles.